Is there anyone out there who can explain (better than the Yaesu manual!) how the automatic ATU works (operationally not electronically) on the Yaesu FT1000MP.

My query is best explained by example:

The AATU has currently matched the antenna (half-size G5RV)with the following VSWR's:

14.260 1:1.214.270 1:1.314.280 1:2.214.290 1:1.314.300 1:2.5

I could understand it if the VSWR increased/decreased steadily as the frequency changed - but not up and down like this.

I assume this is down to the AATU's "memories" - does it store AATU settings for spot frequencies ?

Furthermore, as I am tuning around a specific band the "wait" light comes on (which I would expect) - but I assumed this was re-tuning to the optimum VSWR - this is not so as I can often get a lower VSWR by switching the tuner off then switching it back on again by holding down the tuner button for a second or so (as the manual suggests you do when you use a new antenna).

A brief explanation of the AATU and it's memories would be much appreciated... thanks.

Doesn't make a lot of difference whether it is the Yaesu or any number of automatic COUPLERS. Calling them antenna tuners is a misnomer.

Internally, they sense the line condition (coax, impedance if you please and expressed as Z) and adjust a stepped series of input and/or output capacitors with a stepped series of inductors. This amounts to an LC circuit (or Pi in some cases) to match the 50 ohm Z of the transmitter to what ever Z is impressed at the end of the coax as it enters the rig. This has very little to do with the antenna Z due to the coax type and its length among other things. What ever solution is derived at is stored in memory. Depending upon the band and the algorithm written in to the control circuitry, the "tuner" may retune with small or large excursions of frequency.

For a good explanation of how they work, visit SCG's site at WWW.SGCWORLD.COM.

I suggest if you want to know how the Yaesu's ATU works, you check out the Yaesu reflector on www.contesting.com (go there and look in the left menu area) or the 1000MP reflector on www.qth.net (go there and click "Directory of lists" in the center) - they have a Yaesu list as well.

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